Age and Mass Signatures in the Multiband Second-order Image Structure of Young Star Clusters in M31

The ages and masses of star clusters may leave systematic signatures in the second-order spatial structure of semi-resolved photometric images. To test this hypothesis, we analyze the images using the Hessian matrix and identify basic luminous structures, termed peak cores. Applying this analysis to six-band PHAT/AP images of 1249 M31 clusters with CMD-based ages of 10--300 Myr and masses of 10 2.2 -- 10 4.5,M, we examine the correlations of age and mass with the peak-core structural parameters, C S and Q. Younger clusters show larger C S values in the ultraviolet bands, with the strongest age-- C S anti-correlation in F336W (ρ=-0.61), whereas more massive clusters show smaller Q values, most clearly in F336W (ρ=-0.44). These correlations suggest that the contrast of UV-bright peak cores decreases with age, whereas increasing mass alters the abundance and spatial organization of detectable structures across different bands.